Question

The atomic weights of Be were corrected by Mendeleev using the formula:
(A) $\sqrt v = a(z - b)$
(B) $mvr = \dfrac{{nh}}{{2\pi }}$
(C) Atomic weight = equivalent weight $ \times $ valency
(D) Equivalent weight = Atomic weight $ \times $ valency

Answer 1

Hint: Mendeleev made use of the valency of the atoms in order to correct the atomic weights of some elements. Valency is the number of electrons lost or gained by the atom in the bond formation.

Complete step by step solution:
Many scientists tried to assign the atomic weights to elements. The first of such scientists was Johann Dobereiner. He proposed triads of elements in which three elements were present. He stated that the atomic weight of the atom in the centre is halfway between the weight of the first and the last atom of the trial if we arrange the atoms in increasing atomic weight.
- Then, Alexander Newlands gave a rule of octaves. But this rule was limited up to calcium. The atoms that have more atomic weight than calcium did not follow that rule.
- Then Mendeleev proposed a periodic table in which he arranged the atoms in the order of increasing their atomic weights.
- Mendeleev used the following formula to correct the atomic weight of Be (Beryllium).
Atomic weight = Equivalent weight $ \times $ Valency
- We know that equivalent weight depends upon the valency of the atom. The equivalent weight of an atom can be given by dividing the atomic weight by its valency.

Thus, we can say that the correct answer to this question is (C).

Note: Alongside Be, Mendeleev corrected the weights of elements like Gold, Platinum and Indium. Initially, the atomic weight of Be was supposed to be $13.5$ $gmmo{l^{ - 1}}$ but then using the given formula, Mendeleev proposed new atomic weight of Be which was $9$ $gmmo{l^{ - 1}}$.